According to the method that automatically extracts the region of vertebral body, a medical image incorporating the spinal column obtained by using an X-ray fluoroscopic apparatus and a bone density measuring apparatus and so forth is employed. Hereafter, the inventors set forth the present invention based on a bone-density measuring apparatus as an example.
Relative to the bone-density measuring apparatus, e.g., DXA (Dual Energy X-Ray Absorptiometry) method employs an X-ray beam having two different energy peaks to conduct the measurement. Specifically, an image selectively imaging only bone (low-dose X-ray image) by imaging the lumbar vertebra of a subject (patient) while lying down and bending the knee on the table. The area of an individual vertebra body must be obtained accurately to measure bone density, such as e.g., the bone mineral content, which is an index, indicating the content of minerals contained in bone, which are (e.g., potassium and phosphorus) contained in a specific amount of bone. Then, technologies to automatically extract the area of vertebral body are proposed (e.g., refer to Patent Documents 1-3 and Non-Patent Documents 1-3.)
The extraction of the region roughly comprises two steps including (1) the step of detecting the profile (sideline) and (2) the step of extracting an individual vertebral body by detecting the boundary between vertebral bodies adjacent each other. The present invention relates to the step (2) set forth above. In addition, referring to FIG. 13, the spinal column extends up-and-down in between the cervical vertebra and the pelvis and there is an intervertebral region (intervertebral disc) C in between the vertebral bodies A adjacent each other in addition to the vertebral body A. The boundary between the vertebral bodies A can be detected by drawing a line at the center of the intervertebral region C. Conventionally relative to (2) set forth above, it is deemed that e.g., the pixel values of the constriction location of the profile (sideline) of the lumbar vertebra and of the intervertebral region (when displayed on the monitor, the gradation process renders the pixel value to “brightness”) are low; and the boundary between the vertebrae is being detected by contrast between the vertebrae and by the edge information of upper and lower ends of the vertebrae. In addition, according to the present specification, the pixel value and brightness are taken care equally unless otherwise particularly defined.
In addition, a region called “pedicle of vertebral arch” appears both sides of the upper vertebral body. The pedicle of vertebral arch appears almost always in the upper vertebral body and provides with the higher pixel value than the periphery thereof. According to Patent Document 1, Patent Publication JP 2004-509722 Patent Gazette, the pedicle of vertebral arch is extracted as a landmark, the entire contents of which are incorporated herein by reference.